This paper examines the decline in Illinois public school enrollment that began in 1971-72 and attempts to predict the likely duration and severity of the decline. Much of the paper discusses the use of two different models for calculating enrollment projections from 1974 through 1985. The grade-by-grade model formulates enrollment projections separately for each grade level and then combines those results to project total elementary, total secondary, and total enrollment figures. The aggregate model projects total K-12 enrollment directly from the number of live births for the previous 5 to 17 years. The grade-by-grade projection was calculated assuming a birthrate of 2.1, while the aggregate projection was carried out twice, assuming birthrates of 2.1 and 1.8 respectively. Although results of the three projections differ slightly, they all agree that the enrollment decline in Illinois public schools will continue uninterrupted at least through the fall of 1983, and that enrollment in the fall of 1983 will be at least 16 percent lower than the record high enrollment of 1971. (JG)